Surfaces having low adhesion to ice



Patented Nov. 13, 1951 SURFACES navmc LOW ADHESION 'ro ICE Robert Sinith-Johannsen, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York No Drawing. Application October 26, 1948, Serial No. 56,673

This invention is concerned with decreasing the adhesion of iceto various surfaces. More particularLv, the invention relates to a process for decreasing the adhesion of ice to various surfaces such as glass, plastics, ceramics, metals, treated metallic surfaces, for instance, bonderized surfaces, anodized surfaces, etc., which process comprises (1) treating the aforesaid surface with a silicon-containing composition to provide a coat ing thereon having silicon-bonded OH groups and (2) applying to the aforesaid coated surface a coating comprising a, polyorganihalogenopolysiloxane.

Various methods have been suggested for reducing the adhesion of ice to various surfaces. The reduction of ice adhesion is of particular importance in the refrigeration art, especially in ice cube trays and dividers which are employed for making ice cubes. Although ice cube trays and dividers have been made from various materials, including various metals and plastics, it has been found that for most purposes it is desirable that the ice cube trays and dividers be made of anodized aluminum. However, since anodized aluminum is especially tenacious in its adhesion to ice, it has been found necessary to coat the surfaces of the tray and divider (or grid) with a substantially permanent coating to reduce this adhesion to the ice.

Many coating compositions have been employed for this purpose and to the present time the best found was a wax called Z wax, which is a. high melting hydrocarbon residue obtained during the cracking of gasoline. The "Z" wax referred to above was made by a secret process in Germany and with the advent of World War 11 its importation ceased with the result that there has been a growing need for an equivalent coating for anodized aluminum having the desirable properties found in "Z wax.

I have now discovered that I am able to reduce the adhesion of ice to solid surfaces, including surfaces of anodized aluminum, by applying to the said surface a primer coating which, .in its final form, comprises a silicon-containing composition (i. e., siliceous material) having siliconbonded OH groups, and thereafter applying to the latter coating a polyorganohalogenopolysiloxane. By means of this treatment, I am able to obtain surfaces exhibiting very low adhesion to ice, and which are more durable and more effective than has heretofore been possible to obtain even with the use of Z wax.

I am not unmindful of Patnode Patent 2,306,- 222, issued December 22, 1942, and assigned to 23 Claims. (Cl. 82-1085) the same assignee as the present invention, which discloses and teaches that anodized aluminum especially aluminum ice cube trays and dividers, may be rendered non-wettable by water by treatment of the trays and dividers with vapors of an organohalogenosilane. However, this treatment suggested by the patentee does not have satisfactory durability or permanence, and adhesion to ice increases with each cycle of ice removal.

My invention requires the use of two treatments 'of the surface in order to give the desired results:

First, treatment so as to deposit on the surface a silicon-containing compound containing siliconbonded OH groups, and finally, treatment of the latter coated surface with a polyorg-anohalogenopolysiloxane. If only the polyorganohalogenopolysiloxane is used in the treatment of the surface, it is found that the coating thus deposited is not permanent and the ice release properties are progressively poorer.

In general, the first coating applied to the surface, whether it be metal, glass, ceramics, plastics, etc., should comprise a siliceous primer coating which either per se contains silicon-bonded OH groups or which, upon proper treatmenhyields a surface having silicon-bonded OH groups. It is not clearly understood how this reduction in ice adhesion of a surface is effected by means of my invention. However, it is believed that the silicon-bonded OH groups of the primer coating react with the halogens of the polyorganohalogenopolysiloxane to give a condensation reaction with the subsequent formation of a thin film comprising residues of the latter compound which I are oriented on the surface and which are believed to be the ice-releasing surface. The undercoating or primer is essentially for the purpose of effecting suitable bonding to the polycrganohalogenopolysiloxane of the surface being treated.

In the practice of my invention, I may employ any one of a large number of siliceous primers for the surface being treated. Thus, 'I may use, for instance, various silicates, for example, organosilicates (i. e., orthosilicates where the hydrogens of orthosilicic acid have been replaced by a hydrocarbon radical), for example, tetra-substituted lower alkyl silicates, for instance, methyl silicate, ethyl silicate, propyl silicate, isobutyl silicate, etc.; aryl silicates, for example, phenyl silicate, etc.; aralkyl silicates, for example, benzyl silicate, etc.; alkaryl silicates, e. g., tolyl silicate, etc.; partially hydrolyzed orsanosi-licates. etc. alkali-metal silicates, for example, sodium silicate (for instance, sodium orthosilicate, especially in the form of a water glass solution) potassium silicate, lithium silicate, etc.; partially hydrolyzed alkali-metal silicates; condensed silicic acid, etc.

Another class of compounds which have been found especially suitable as a primer coating in my claimed invention is one embraced by the general formula SIQCIMRJH where R is a monovalent hydrocarbon radical (for instance, an alkyl, aryl, alkaryl and aralkyl radical) and n is an integer equal to from 1 to 6. Preferably, R is a methyl group and n is at most 4. Of particular value is a fraction comprising essentially a mixture of compounds embraced by the aforementioned formula which is obtained as a high boiling residue (boiling point from about 140 to 163 0., especially from approximately 150 to 160 C.) in the preparation of methylchlorosilanes by the passage of methyl chloride over heated silicon in the presence of a suitable catalyst in accordance with the procedure disclosed and claimed in Rochow Patent 2,380,995, issued August 7, 1945 and assigned to the same assignee as the present invention. Examples of compounds covered by the aforementioned formula where R is a methylgroup and which are found in the mixture obtained in the high boiling residue described above may be. for instance, hexachlorodisilane, methylpentachlorodisilane, tetramethyldichlorodisilane, dimethyltetrachlorodisilane, etc. Instead of the mixture of chlorodisilanes, it will, of course, be apparent to those skilled in the art that other individual or mixtures of halogenodisilanes may also be employed without departing from the scope of the invention, the specific halogenodisilanes obtained depending upon the particular organic halide employed for passage over the heated silicon.

In addition to the methylhalogenodisilanes described above, other organohalogenodisilanes may also be employed, for example, dipl'ienyltetrachlorodisilane, triphenyltrichlorodisilane, tetraphenyldichlorodisilane, ditolyltetrabromodisilane, diethyltetrabromodisilane, tetraethyldichlorodisilane, diamyltetrachlorodisilane, etc.

As pointed out previously, organohalogenosilones by themselves do not give the desired results. However, I have found out that I can use organohalogenosilanes, especially aryl halogenosilanes and alkyl halogenosilanes containing at least four "carbon atoms in the alkyl group as primers for rendering surfaces less adherent to ice, if, after application to the surface-I hydrolyze the organohalogenosilanes with water to convert them to a film containing siliconbonded OH groups. This primer coating is then intimatedly contacted with a polyorganohalogenopolysiloxane in the same manner as described above. Among organohalogenosilanes which have been-successfully employed for this purpose may be mentioned, for instance, phenyltrichlorosilane, diphenyldichlorosilane, pentyltrichlorosilane, etc.

A still further class of compound which may be employed as a primer coating for the polyorganohalogenopolysiloxane comprises organopolysiloxanes containing silicon-bonded halogens which, when applied to the surface and hydrolyzed, yield coatings which are especially amenable as a result of the treatment with the poly- 4. organohalogenopolysiloxane to yield coated surfaces having outstandingly low adhesion to ice. Among such compositions may\be mentioned, for instance, partially hydrolyzed methyltrichlorosilane (obtained by hydrolyzing methyltrichlorosilane in an amount of water insufflcient to completely hydrolyze the hydrolyzable halogen atoms so that a polysiloxane linkage is obtained wherein is present silicon-bonded methyl groups and a small proportion of silicon-bonded chlorine atoms, there being present an average of from about 0.9 to 1.2 methyl groups per silicon atom. The use of such partially hydrolyzed material as a primer coating alone has given outstanding results in my claimed process and has afforded good control in processing.

Especially good results have beenobtained in using as the primer coating a mixture comprising (1) an organosilicate, for example, ethyl silicate, and a disilane corresponding to the general formula SiilC1n(CH3)B-n where n is an integer equal to from 1 to 6. In the use of such a primer, although the proportions of the ingredients may be varied within wide limits, good results are obtained when the organosllicate, for example, ethyl silicate, is present, by weight, in an amount equal to from about 5 to 50 per cent or higher of the total weight of the organosilicate and the disilane.

Additional compositions which may be employed as the primer coating are, e. g., hexachlorodisiloxane, hexabromodisiloxane, dimethyltetrachlorodisiloxane, etc. These compositions, of course, on hydrolysis yield a surface having silicon-bonded OH groups.

The polyorganohalogenopolysiloxanes (either individually or mixtures thereof) employed as treating agents in the claimed process and methods of preparing the same are more specifically disclosed and claimed in Sauer Patent 2,421,653. issued June 3, 1947 and Patnode Patent 2,381,366, issued August 7, 1945, both assigned to the same assignee as the present invention. As will be apparent from a reading of these patents, especially the Sauer patent, it is possible to prepare many different types of polyorganohalogenopolysiloxanes, depending upon the particular hydrocarbon-substituted polysiloxane and organohalogenosilane employed as the reactants. Additional examples of polyorgandhalogenopolysiloxanes in addition to those disclosed in the aforementioned patents which may also be used in the instant claimed invention are tetramethyl- 1,2-dibromodisiloxane, tetraethyl-L2-dibromodisiloxane, hexabutyl-1,3-difiuorotrisiloxane, tetraphenyl-1,2-dichlorodisiloxane, etc. The polycrganohalogenopolysiloxanes are generally characterized by the fact that they are for the most part linear and contain terminal silicon-bonded halogens and have an average ratio of from about 1.9 to 2.0 organic groups (for instance, methyl groups) per silicon atom.

The general procedure for treating a particular surface to render it less adherent to ice comprises coating the surface, for instance, as by dipping, with the particular primer or solution of the primer employed for the purpose, using for instance, from about a 0.1 to 25 per cent solution of the primer. Thereafter, again depending on the primer used, the coated surface may be exposed for a varying length of time to the air so that hydrolysis of silicon-bonded hydrolyzable groups (for instance, silicon-bonded halogens,

amino groups, alkoxy radicals, etc.) found in the primer coating can be effected to yield a surface 'genopolysiloxane. 'genopolysiloxane per se may be employed for this comprising the aforementioned silicon-containing composition having silicon-bonded OH groups. In some cases it may be desirable to-contact the primed coating with water, such as in the form of a liquid or a vapor, to accelerate the hydrolysis step and to remove undesirable hydrolysis byproducts, such as, hydrogen halide. In other cases, especially in the case of alkali-metal silicates and water solutions of such silicates, immersion of the surface being treated in such solutions yields a coating already containing siliconbonded OH groups because of the fact that in a water solution, alkali-metal silicates are at least partially hydrolized to give hydroxyl groups attached directly to silicon atoms.

After treatment of the surface with the primer coating and the employment of any steps necessary to obtain a surface having silicon-bonded OH groups, the treated surface is then contacted, for example, by dipping, with the organohalo- Although the organohalotreatment, it has been found desirable to use dilute solutions, of the order of from about 1 to per cent, by weight, of the organohalogenopolysiloxane in a non-aqueous solvent, for example, dry toluene, benzene, xylene, etc. It is, of course, apparent that other organic solvents free of moisture, for instance, diethyl ether of ethylene glycol, etc., may also be employed without .departing from the scope of this invention.

After the treatmen" with the organohalogenopolysiloxane, the surface is then allowed to drain free of any traces of the last treating material and air-dried to take advantage of moisture in the air whereby any residual hydrolyzable groups may be converted to the hydrolyzed state. This air drying operation is allowed to proceed for a sufiicient time to permit interaction between the silicon-bonded OH groups and the silicon-bonded halogens of the polyorganohalcgenopolysiloxane. Thereafter the final surface is washed with water, for instance, by immersing the same in water to assure completion of the hydrolysis and to remove traces of hydrogen halide. This washing operation may require anywhere from a few minutes to several hours.

In priming the surface with any one of the silicates described above, a slightly different procedure is employed from that used with many of the other priming coatings. Thus, in the case of the alkali-metal silicates, I may use a water solution, for example, in the form of a 2 to 30 per cent, by weight, solids solution of the alkalimetal silicate. Greater or smaller concentrations may be employed without departing from the scope of my invention. In the case of the organosilicates, I have found it advantageous to employ the latter in the pure state, although it is within the scope of this invention to use solutions of the same in inert solvents, for example, in suitable organic solvents, for instance, alcohol, ethyl ether, etc

After treatment of the surface with the silicate, the object is preferably allowed to air dry for a period of, for example, from thirty seconds to one to two hours or more in order to allow the silicate to set. Thissetting period renders the silicate coating relatively insoluble with regard to the solution of the polyorganohalogenopolysiloxane which is next applied as a coating. The attainment of this state is desirable in order to minimize contamination of the polyorganohalogenopolysiloxane.

Thereafter the silicate-treated surface is dipped in the polyorganohalogenopolysiloxane which is preferably in the form of a dilute solution, for example, in the form of from a 0.1 to 25 per cent. by weight, solution, or an even higher concentration in an inert solvent, for instance, an arcmatic or aliphatic hydrocarbon solvent. This latter treatment may be accomplished by dipping the silicate-coated surface in the polyorganohalogenopolysiloxane solution for a period of from about 10 to'45 seconds.

The treated article is preferably allowed to stand exposed. to the air for a sufllcient length of time, for example, from 2 to 36 hours or more,

in order that the polyorganohalogenopolysiloxane may be converted by the small amount of moisture in the air to a composition of matter having substantially no halogens (that is, hydrolyzable halogens) attached to a silicon and relatively few, if any, hydroxyl groups present as a result of any hydrolysis which might take place.

The same general procedure as described above is also employed for priming surfaces with organosilicon compounds containing hydrolyzable groups as, for instance, dimethyltetrachlcrodisilane, tetramethyldichlorodisilane, mixtures of halogenated disilanes as obtained, for example, in the high boiling residue resulting from the passage of methyl chloride over heated silicon, partially hydrolyzed methyltrichlorosilane, etc. In many cases, it has been found expedient, prior to priming the surface, to warm the surface to remove any excess moisture in order to obtain better homogeneity of the primer coating and to permit better adhesion of the silicon-containing compound to the surface.

In order that those skilled in the art may better understand how the present invention may be practiced, the following examples are given by way of illustration and not by way of limitation. All parts are by weight.

Example 1 weight, toluene solution of a mixture of polymethylchloropolysiloxanes comprising the product of reaction obtained by heating under pressure at a temperature of about 400 C. a mixture consisting of approximately equal parts, by weight, of dimethyldichlorosilane and the product of hydrolysis of dimethyldichlorosilane (see aforementioned Sauer Patent 2,421,658); that fraction of the reaction product comprising essentially a mixture of polymethylchloropolysiloxanes was isolated and employed in the aforesaid treatment. Thereafter the treated tray and divider were allowed to remain exposed to the air for about 24 hours. A smooth transparent coating was obtained. Whenwater was frozen in the treated tray and divider, the ice cubes formed could be removed by application of a relatively small pressure. After ice removal cycles, it was working as satisfactorily as it did in the beginning and no apparent change in the force required to remove the ice cubes could be detected.

. Example 2 In this example an anodized aluminum ice cube tray and divider were treated in exactly the same manner as was done in Example'i with the exception that the water glass solution comprised per cent, by weight, solids. As a control another tray and divider were treated with "Z" wax and each of the two assemblies was employed to freeze water in the form of ice cubes and the pressure required to remove the formed ice cubes in each case was measured. The results established that after about ice removals. the force required to remove the ice cubes from the tray and divider treated in accordance with my invention was essentially the same throughout the test and equal, on the average. to the best values obtained with Z wax. However. whereas the force required for removal of the ice cubes in the first instance remained fairly constant, in the case of the Z wax force required was increasing at the end of the 25 ice removals. In addition, the ice cubes could be removed intact without any evidence of ice adhering to the surfaces of the tray or divider. In contrast to this, the tray and divider treated with the "Z" wax contained particles of adhering ice after the ice cubes were removed and, what was more disadvantageous, many of the ice cubes shattered or were broken when they were removed from the ice cube tray.

Example 3 An anodized aluminum tray and divider were immersed in tetraethyl silicate and allowed to air-dry for about 1 hour. Thereafter they were dipped in a 10 per cent toluene solution of the polymethylchloropolysiloxane described in Exampie 1 and allowed to remain immersed for about to 45 seconds and then removed. The tray and divider were allowed to stand exposed to the air for about 12 hours to yield a transparent, smooth coating. After about 45 removals of ice cubes frozen in this tray, it was found that the force required to remove the cubes was much less than that required to remove ice cubes from trays and divider coated with Z wax. In addition, the ice cubes were removed easily without breakage and without any remnants of ice adhering to the divider.

Example 4 A glass slide was warmed to remove any excess moisture and was then dipped into a dry 1 per cent toluene solution of a high boiling residue having a boiling point of about 140 to 163 C. obtained in the reaction between methyl chloride and heated silicon at a temperature of about 250 to 300 C. using copper as a catalyst in accordance with the process described and claimed in the aforementioned Rochow Patent 2,380,995. This high boiling residue was a mixture of chlorodisilanes, of which from about 85 to 95 per cent comprised dimethyltetrachlorodisilane (including its various isomers, such as, for instance, 1,2- dimethyl 1.1.2.2 tetrachlorodisilane. 1.1 dimethyl-1,2,2,2-tetrachlorodisilane, etc.) as well as small amounts of hexachlorodisilane, methylpentachlorodisilane, trimethyltrichlorodisilape, and tetramethyldichlorodisilane. The treated glass surface was then air-dried for about five minutes until the surface was dry and thereafter the slide was dipped in a dry 10 per cent, by weight,

toluene solution of a composition comprising a mixture of polymethylchloropolysiloxanes referred to in Example 1. The latter dippin operation was for a period of about 3 in 10 seconds. Thereafter, the glass slide was removed and allowed to again air dry until the surface was dry some cases it was necessary to shatter the ice pellet to remove it from the surface of the glass.

Treatment of a glass slide only with the polymethylchloropolysiloxane gave an unsatisfactory ice release surface, which although it was hydrophobic, exhibited poor ice release properties.

Example 5 An adodized aluminum ice cube tray and divider were dipped in an approximately i per cent, by weight, toluene solution of the mixture of chlorodisilanes employed in Example 4 and obtained as a. high boiling residue inthe manufacture of methylchlorosilanes. Thereafter the tray and divider were allowed to air dry for about 15 minutes, dipped in a 10 per cent toluene solution of a mixture of polymethylchloropolysiloxanes using the same procedure and materials as described in Example 3. Thereafter the tray and divider were air dried until dry (about 1 hour) and washed by immersion in water for about 4 hours. Using this ice cube tray and divider, it

was found that ice cubes could be frozen and thereafter released from the ice cube tray and from the divider by exerting only a small amount of pressure. In addition, it was also found that the ice cubes could be removed in one piece without any shattering occurring, and thatthe surfaces of the tray and divider were free of any adhering ice.

In order to compare the results of using the process described in this example with those of using a wax-coated ice cube tray and divider, the wax specifically being an animal wax identified as Barco wax, a tray and divider were also coated with the latter wax and the two sets of trays and dividers were subjected to freezing tests by filling each tray and divider with water and successively releasing and refreezing ice cubes. In the case of the use of my claimed process, it was found that the average force required to release the ice cubes 'after 40 cycles was about $5 units of force, whereas, under equivalent test conditions. the tray and divider treated with Barco-wax required a force of about 11 units of force. In addition, the cubes released from the tray treated in accordance with my process were whole and uncracked, and no ice clung to the divider. In contrast to this, the Barco wax-coated tray exhibited such a high adhesion to the ice cubes that in releasing the latter they cracked; in addition, it was found that slivers of ice clun to the divider, thus preventing clean removal of the ice cubes.

Example 6 In this example an anodized aluminum ice cube tray and divider were treated in essentially the same manner as that employed in Example 5 with the exception that instead of the high boiling residue employed for priming the surface of the tray and divider, there was employed hexachlorodisilane. The finally treated anodized aluminum ice cube tray and divider had properties which were essentially the same as the properties of the ice cube tray and divider obtained in Example 5, and frozen ice cubes could be released therefrom tothetouchandthenimmersedandwashedin byalightpressurewithoutcracking of theice cubes or there remaining any particles of ice clinging to the divider.

Example 7 An anodized aluminum ice cube tray and divider were treated in essentially the same manner as that described in Example with the exception that hexachiorodisiloxane was used in place of the high boiling residue employed there. The results obtained were substantially the same as those of the ice cube tray and divider treated as described in Example 5.

Example 8 With the exception of the substitution of dimethyltetrachlorodisilane (boiling point 157.2 C.) for the high boiling residue in Example 5, an anodized aluminum ice cube tray and divider were treated exactly as the tray and divider in Example 5 with equivalent results.

Example 9 In this example silicon tetrachloride, phenyltrichlorosilane, pentyltrichlorosilane, decachlorotetrasilane, and diphenyldichlorosilane were each used in place of the high boiling residue of Example 5 as a primer coating for anodized aluminum ice cube trays and dividers. Withthe exception of this one deviation, the trays and dividers were treated further in the same manner as were the tray and divider in Example 5 to yield an article whose properties were essentially the same as those of the ice cube tray and divider obtained in Example 5.

Example 10 In this example an anodized aluminum ice cube tray and divider were treated in the same manner as described in Example 5 with the exception that a partially hydrolyzed methyltrichlorosilane resin (methyl-to-silicon ratio of 1) dissolved in diethyl ether of ethylene glycol was used as a primer in place of the high boiling residue used in Example 5. The successive treating steps were the same as that described in Example 5. The final coated surface obtained was especially smooth and was very effective in reducing the adhesion of ice to the surface.

Example 11 A mixture was prepared by combining, by weight, about 10 parts ethyl silicate and 90 parts of the high boiling residue described in Example 5. This mixture was dissolved in dry toluene to make a 5 per cent solution. An anodized aluminum ice cube tray and divider were first warmed to remove any excess moisture and thereafter dipped for a few seconds in the above-described toluene solution. The tray and divider were removed, air-dried for several minutes, and then dipped in a 10 per cent toluene solution of a mixture of polymethylchloropolysiloxanes described in Example 5, and again air-dried until the surface was dry to the touch. The tray and divider were then submerged in water for about 5 to 7 hours and thereafter dried. When ice cubes were frozen in this ice cube tray and divider. it was found that they could be removed with only slight pressure and that the ice cubes came out clean without any evidence of clinging particles of ice to the divider or tray.

It will, of course, be apparent to those skilled in the art that in addition to glass and aluminum surfaces described above, other surfaces may also be treated in accordance with my claimed process to yield products exhibiting low adhesion to ice.

inexpensive materials which are readily avail able in good quantity.

In addition to the use for treating ice cube trays and dividers described above. my invention may also be employed in cold box liners and evaporator units in refrigerators, on propellers, on windshields, on electrical conductors, etc., where it is desired to minimize the adhesion of ice to the surfaces of these various articles.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. The process of lowering the adhesion of ice to a surface which comprises (1) treating the surface with a silicon-containing composition convertible by moisture to a composition containing a silicon-bonded OH group and selected from the class consisting of organosilicates, alkali-metal silicates, condensed silicic acid, inorganic halogenodisilanes, organohalogenodisilanes, and mixtures thereof, and effecting hydrolysis ofthe aforesaid silicon-containing composition thereby to provide a coating thereon containing siliconbonded OH groups and (2) applying a preformed polyorganohalogenopolysiloxane containing a terminal silicon-bonded halogen tovthe coated surface.

2. The process of lowering the ice adhesion of a metallic surface which comprises (1) forming on the said surface a coating of a silicon-containing compound convertible by moisture to a composition containing a silicon-bonded OH group, and selected from the class consisting of organosilicates, alkali-metal silicates, condensed silicic acid, inorganic halogenodisilanes, organohalogenodisilanes, and mixtures thereof, and effecting hy- (2) hydrolyzing the aforesaid organosilicate surface to give a coating in which there are present silicon-bonded OH groups and (3) treating the hydrolyzed surface with a preformed polyorganohalogenopolysiloxane containing a terminal silicon-bonded halogen.

4. The process of lowering the ice adhesion of a metallic surface which comprises (1) applying to the said surface an alkali-metal silicate containing silicon-bonded OH groups and (2) treating the said coated metallic surface obtained in (1) with a preformed polyorganohalogenopolysiloxane containing a terminal silicon-bonded halogen.

5. The process of lowering the ice adhesion of a metallic surface which comprises (1) applying to the said surface a coating of sodium silicate containing silicon-bonded OH groups and (2) treating the said coated surface obtained in '(l) with a preformed polymethylhalogenopolysiloxane containing a terminal silicon-bonded halogen.

6. The process of lowering the ice adhesion of a metallic surface which comprises (1) coating the said surface with ethyl silicate, (2) effecting hydrolysis of some of the silicon-bonded ethoxy radicals to give a surface containing siliconbonded OH groups by exposing the said surface to a moist atmosphere and (3) treating the said hydrolyzed surface with a preformed poiymethylhalogenopolysiloxane containing a terminal silicon-bonded halogen.

7. The process of-lowering the ice adhesion of a metallic surface which comprises (1) applying to the said surface a composition of matter comprising a disilane consisting essentially of silicon atom. organic radicals bonded to silicon atoms by carbon-silicon linkages, and silicon-bonded halogen atoms, (2) hydrolyzing the treated surface obtained in (1) with water to give a surface containing silicon-bonded OH groups, and (3) treating the said hydrolyzed surface with a preformed polymethylhalogenopolysiloxane containing a terminal silicon-bonded halogen.

8. The process of lowering the ice adhesion of a metallic surface which comprises (1) applying to the said surface a coating of sodium silicate containing silicon-bonded OH groups and (2) treating the said coated surface with a preformed polymethylchloropolysiloxane containing a terminal silicon-bonded chlorine.

9. The process of reducing the tendency of ie to adhere to a metallic surface which comprises (i) treating the said surface with ethyl silicate, (2) allowing hydrolysis of the ethyl silicate to take place by exposing the aforesaid treated sur face to an atmosphere containing moisture to giva surface having silicon-bonded OH groups, and (3) treating the said hydrolyzed surface with a preformed polymethylchloropolysiloxane containing a terminal silicon-bonded chlorine atom.

10. The process of reducing the tendency of ice-to adhere to a metallic surface which comprises 1) applying to the said surface a composition comprising a chloromethyldisilane consisting essentially of silicon atoms, methyl radicals attached directly to silicon atoms by carbonsilicon linkages, and silicon-bonded chlorine atoms, (2) hydrolyzing the aforesaid coated surface obtained in (1) with water to give a surface having silicon-bonded OH groups and (3) treating the said hydrolyzed surface with a preformed polymethylchloropolysiloxane containing a terminal silicon-bonded chlorine atom.

11. The process of lowering the ice adhesion of an anodized aluminum ice cube tray and divider which comprises 1) applying to the surfaces of the aforesaid ice cube tray and divider a. coating comprising sodium silicate containing siliconbonded OH groups and (2) treating the said coated surfaces with a preformed polymethylchloropolysiloxane containing a silicon-bonded chlorine atom.

12. The process of reducing the tendency of ice cubes to adhere to an aluminum ice cube tray and divider having anodized surfaces which comprises (1) applying to the surfaces of the aforesaid ice cube tray and divider a composition of matter comprising ethyl silicate, (2) hydrolyzing the ethyl silicate by exposing the aforesaid surfaces to an atmosphere containing moisture to provide a coating containing silicon-bonded OH group and (3) treating the said hydrolyzed surfaces with a preformed polymethylchloropolysiloxane containing a terminal silicon-bonded chlorine atom.

13. The process of lowering the ice adhesion of ice cubes to an anodized ice cube tray and divider which comprises (1) applying to the said surfaces a solution containing dimethyltetrachlor dhilfiiifi 12 r (2) hydrolyzing-the said coated surfaces to provide a coating containing silicon-bonded OH groups, and (3) treating the hydrolyzed surfaces with a preformed polymethylchioropolyslloxane 022 8 a terminal silicon-bonded chlorine a m.

14. The process of reducing the tendency of ice cubes to adhere to the surfaces of an aluminum ice cube tray and divider which comprises (1) applying to the aforesaid surfaces a composition of matter comprising ethyl silicate and dimethyl-- tetrachlorodisilane, (2) hydrolyzing the said treated surfaces with water to provide a coating on the aforesaid surfaces containing siliconbonded OH groups, and (3) immersing the hydrolyzed surfaces in a solution comprising a preformed polymethylchloropolysiloxane containing a terminal silicon-bonded chlorine atom.

15. A solid surface exhibiting low adhesion to ice, the said surface containing a series of coatings comprising 1) a silicon-containing composition having silicon-bonded OH groups and selected from the class consisting of hydrolyzed organo-silicates, alkali-metal silicates, condensed silicic acid, inorganic halogenodisilanes, organohalogenodisilanes, and hydrolyzed mixtures thereof, and (2) another coating comprising a preformed polyorganohalogenopolysiloxane containing a terminal silicon-bonded halogen atom and superimposed directly on the coating of (1) 16. A metallic surface exhibiting improved resistance to adhesion of ice, said surface containing a series of coatings comprising (1) a silicate coating applied directly to the said surface having silicon-bonded OH groups, and 2) another coating comprising a preformed polyorganohalogenopolysiloxane containing a terminal silicon-bonded halogen atom, the said polyorganohalogenopolysiloxane being superimposed directly on the aforementioned silicate coating.

' 1'7. A metallic surface exhibiting improved resistance to adhesion of ice, said surface containing a series of coatings comprising (i) ethyl silicate applied directly to the said surface containg silicon-bonded OH groups, and (2) another coating comprising a preformed polyorganohalogenopolysiloxane containing a terminal silicon-bonded halogen atom and superimposed directly on the aforementioned silicate coating.

18. A metallic surface exhibiting decreased adhesion to ice, the said surface containing a series of coatings comprising (1) an organohalogenodisilane consisting of organic groups connected to silicon atoms by carbon-silicon linkages, silicon atoms, and silicon-bonded halogen atoms, the said disilane having been hydrolyzed after application to the metallic surface to give a coating containing silicon-bonded OH groups, and 2) another coating comprising a preformed polyorganohalogenopolysiloxane containing a terminal silicon-bonded halogen atom and superimposed directly on the surface of the hydrolyzed disilane described above.

19. A metallic surface exhibiting decreased adhesion to ice, the said surface containing a series of coatings comprising (1) a sodium silicate coating containing silicon-bonded OH groups applied directly to the said surface and (2) another coating comprising a preformed polyorganohalogenopolysiloxane containing a terminal silicon-bonded halogen'atom, the said polyorganohalogenopolysiloxane being superimposed directly on the aforementioned silicate coating.

20. An aluminum ice cube tray and divider having an anodized aluminum surface and exhibiting decreased adhesion to ice, the surfaces of said tray and divider having applied thereto a series of coatings comprising (1) a coating of ethyl silicate having silicon-bonded OH groups, and (2) another coating comprising a preformed polymethylchloropolysiloxane containing a terminal silicon-bonded chlorine atom, said polymethylchloropolysiloxane being applied directly to the aforesaid silicate coating.

21. A refrigerator aluminum ice cube tray and divider having an anodized aluminum surface and exhibiting decreased adhesion to ice, the surfaces of said tray and divider having applied thereto a series of coatings comprising (1) a coating comprising dimethyltetrachlorodisilane which has been hydrolyzed after application to the surfaces to give a coating containing silicon-bonded OH groups, and (2) a coating comprising a preformed polymethylchloropolysiloxane containing a silicon-bonded chlorine atom and superimposed directly on the aforesaid hydrolyzed coating.

22. A refrigerator ice cube tray and divider having a surface of anodized aluminum and ex hibiting decreased adhesion to ice, the surfaces of said tray and divider having applied thereto a series of coatings comprising (1) a coating of sodium silicate containing silicon-bonded OH groups and (2) a coating comprising a preformed polymethylchloropolysiloxane containing a terminal silicon-bonded chlorine atom and superimposed directly on the aforesaid silicate coating.

23. A refrigerator ice cube tray and divider having a surface of anodized aluminum and exhibiting decreased adhesion to ice, the surfaces of said tray and divider having applied thereto a series of coatings comprising (1) a coating comprising a mixture of ingredients comprising ethyl silicate and dimethyltetrachlorodisilane, the said coating having been hydrolyzed on the surface so as to form silicon-bonded OH groups and (2) a coating comprising a preformed polymethylchloropolysiloxane containing a terminal siliconbonded chlorine atom, the said polymethylchloropolysiloxane atom being applied directly to the aforesaid hydrolyzed silicate and disilane coating.

ROBERT SMITH-JOHANNSE'N.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,306,222 Patnode Dec. 22, 1942 2,405,988 Barry Aug. 20, 1946 2,412,470 Norton Dec. 10, 1946 2,418,935 Hutchison Apr. 15, 1947 2,436,304 Johannson Feb. 17, 1948 2,438,736 Barry May 30, 1948 2,471,224 Loughborough May 24, 1949 

1. THE PROCESS OF LOWERING THE ADHESION OF ICE TO A SURFACE WHICH COMPRISES (1) TREATING THE SURFACE WITH A SILICON-CONTAINING COMPOSITION CONVERTIBLE BY MOISTURE TO A COMPOSITION CONTAINING A SILICON-BONDED OH GROUP AND SELECTED FROM THE CLASS CONSISTING OF ORGANOSILICATES, ALKALI-METAL SILICATES, CONDENSED SILICIC ACID, INORGANIC HALOGENODISILANES, ORGANOHALOGENODISILANES, AND MIXTURES THEREOF, AND EFFECTING HYDROLYSIS OF THE AFORESAID SILICON-CONTAINING COMPOSITION THEREBY TO PROVIDE A COATING THEREON CONTAINING SILICONBONDED OH GROUPS AND (2) APPLYING A PREFORMED POLYORGANOHALOGENOPOLYSILOXANE CONTAINING A TERMINAL SILICON-BONDED HALOGEN TO THE COATED SURFACE. 